Microdialysis in freely moving mice: determination of acetylcholine, serotonin and noradrenaline release in galanin transgenic mice

Serotonergic neuromodulation of synaptic plasticity

Synaptic plasticity constitutes a fundamental process in the reorganization of neural networks that underlie memory, cognition, emotional responses, and behavioral planning. At the core of this phenomenon lie Hebbian mechanisms, wherein frequent synaptic stimulation induces long-term potentiation (LTP), while less activation leads to long-term depression (LTD). The synaptic reorganization of neuronal networks is regulated by serotonin (5-HT), a neuromodulator capable of modify synaptic plasticity to appropriately respond to mental and behavioral states, such as alertness, attention, concentration, motivation, and mood. Lately, understanding the serotonergic Neuromodulation of synaptic plasticity has become imperative for unraveling its impact on cognitive, emotional, and behavioral functions. Through a comparative analysis across three main forebrain structures-the hippocampus, amygdala, and prefrontal cortex, this review discusses the actions of 5-HT on synaptic plasticity, offering insights into its role as a neuromodulator involved in emotional and cognitive functions. By distinguishing between plastic and metaplastic effects, we provide a comprehensive overview about the mechanisms of 5-HT neuromodulation of synaptic plasticity and associated functions across different brain regions.

Label free impedance based acetylcholinesterase enzymatic biosensors for the detection of acetylcholine

Realtime monitoring of neurotransmitters is of great interest for understanding their fundamental role in a wide range of biological processes in the central and peripheral nervous system, as well as their role, in several degenerative brain diseases. The measurement of acetylcholine in the brain is particularly challenging due to the complex environment of the brain and the low concentration and short lifetime of acetylcholine. In this paper, we demonstrated a novel, label-free biosensor for the detection of Ach using a single enzyme, acetylcholinesterase (ACHE), and electrochemical impedance spectroscopy (EIS). Acetylcholinesterase was covalently immobilized onto the surface of gold microelectrodes through an amine-reactive crosslinker dithiobis(succinimidyl propionate) (DSP). Passivation of the gold electrode with SuperBlock eliminated or reduced any non-specific response to other major interfering neurotransmitter molecules such as dopamine (DA), norepinephrine (NE) and epinephrine (EH). The sensors were able to detect acetylcholine over a wide concentration range (5.5-550 μM) in sample volumes as small as 300 μL by applying a 10 mV AC voltage at a frequency of 500 Hz. The sensors showed a linear relationship between Ach concentration and ΔZmod(R2 = 0.99) in PBS. The sensor responded to acetylcholine not only when evaluated in a simple buffer (PBS buffer) but in several more complex environments such as rat brain slurry and rat whole blood. The sensor remained responsive to acetylcholine after being implanted ex vivo in rat brain tissue. These results bode well for the future application of these novel sensors for real time in vivo monitoring of acetylcholine.

Rice-memolin, a novel peptide derived from rice bran, improves cognitive function after oral administration in mice

Many people eat polished rice, while rice bran, a by-product known to be rich in protein and expected to have potential functions for health benefits, has not been effectively utilized. In this study, we determined that orally administered Val-Tyr-Thr-Pro-Gly (VYTPG) derived from rice bran protein improved cognitive decline in mice fed a high-fat diet (HFD). It was demonstrated that VYTPG was released from model peptides corresponding to fragment sequences of original rice proteins (Os01g0941500, Os01g0872700, and allergenic protein) after treatment with thermolysin, a microorganism-derived enzyme often used in industrial scale processes. The thermolysin digest also improved cognitive decline after oral administration in mice. Because VYTPG (1.0 mg/kg) potently improved cognitive decline and is enzymatically produced from the rice bran, we named it rice-memolin. Next, we investigated the mechanisms underlying the cognitive decline improvement associated with rice-memolin. Methyllycaconitine, an antagonist for α7 nicotinic acetylcholine receptor, suppressed the rice-memolin-induced effect, suggesting that rice-memolin improved cognitive decline coupled to the acetylcholine system. Rice-memolin increased the number of 5-bromo-2'-deoxyuridine (BrdU)-positive cells and promoted the mRNA expression of EGF and FGF-2 in the hippocampus, implying that these neurotropic factors play a role in hippocampal neurogenesis after rice-memolin administration. Epidemiologic studies demonstrated that diabetes is a risk factor for dementia; therefore, we also examined the effect of rice-memolin on glucose metabolism. Rice-memolin improved glucose intolerance. In conclusion, we identified a novel rice-derived peptide that can improve cognitive decline. The mechanisms are associated with acetylcholine and hippocampal neurogenesis. Rice-memolin is the first rice-brain-derived peptide able to improve cognitive decline.

Galanin's implications for post-stroke improvement

Stroke leads to a variety of pathophysiological conditions such as ischemic infarct, cerebral inflammation, neuronal damage, cognitive decline, and depression. Many endeavors have been tried to find the therapeutic solutions to attenuate severe neuropathogenesis after stroke. Several studies have reported that a decrease in the neuropeptide regulator ‘galanin’ is associated with neuronal loss, learning and memory dysfunctions, and depression following a stroke. The present review summarized recent evidences on the function and the therapeutic potential of galanin in post-ischemic stroke to provide a further understanding of galanin's role. Hence, we suggest that galanin needs to be considered as a therapeutic factor in the alleviation of post-stroke pathologies.

The frontal cortex as a network hub controlling mood and cognition: Probing its neurochemical substrates for improved therapy of psychiatric and neurological disorders

The highly-interconnected and neurochemically-rich frontal cortex plays a crucial role in the regulation of mood and cognition, domains disrupted in depression and other central nervous system disorders, and it is an important site of action for their therapeutic control. For improving our understanding of the function and dysfunction of the frontal cortex, and for identifying improved treatments, quantification of extracellular pools of neuromodulators by microdialysis in freely-moving rodents has proven indispensable. This approach has revealed a complex mesh of autoreceptor and heteroceptor interactions amongst monoaminergic pathways, and led from selective 5-HT reuptake inhibitors to novel classes of multi-target drugs for treating depression like the mixed α₂-adrenoceptor/5-HT reuptake inhibitor, S35966, and the clinically-launched vortioxetine and vilazodone. Moreover, integration of non-monoaminergic actions resulted in the discovery and development of the innovative melatonin receptor agonist/5-HT_2C receptor antagonist, Agomelatine. Melatonin levels, like those of corticosterone and the "social hormone", oxytocin, can now be quantified by microdialysis over the full 24 h daily cycle. Further, the introduction of procedures for measuring extracellular histamine and acetylcholine has provided insights into strategies for improving cognition by, for example, blockade of 5-HT₆ and/or dopamine D₃ receptors. The challenge of concurrently determining extracellular levels of GABA, glutamate, d-serine, glycine, kynurenate and other amino acids, and of clarifying their interactions with monoamines, has also been resolved. This has proven important for characterizing the actions of glycine reuptake inhibitors that indirectly augment transmission at N-methyl-d-aspartate receptors, and of "glutamatergic antidepressants" like ketamine, mGluR5 antagonists and positive modulators of AMPA receptors (including S47445). Most recently, quantification of the neurotoxic proteins Aβ42 and Tau has extended microdialysis studies to the pathogenesis of neurodegenerative disorders, and another frontier currently being broached is microRNAs. The present article discusses the above themes, focusses on recent advances, highlights opportunities for clinical "translation", and suggests avenues for further progress.

Galanin and Cognition

Since the neuropeptide galanin’s discovery in 1983, information has accumulated that implicates it in a wide range of functions, including pain sensation, stress responses, appetite regulation, and learning and memory. This article reviews the evidence for specific functions of galanin in cognitive processes. Consistencies as well as gaps in the literature are organized around basic questions of methodology and theory. This review shows that although regularities are evident in the observed behavioral effects of galanin across several methods for measuring learning and memory, generalization from these findings is tempered with concerns about confounds and a restricted range of testing conditions. Furthermore, it is revealed that many noncognitive behavioral constructs that are relevant for assessing potential roles for galanin in cognition have not been thoroughly examined. The review concludes by laying out how future theory and experimental work can overcome these concerns and confidently define the nature of the association of galanin with particular cognitive constructs.

The 5-hydroxytryptamine4 receptor enables differentiation of informational content and encoding in the hippocampus

Long‐term synaptic plasticity, represented by long‐term depression (LTD) and long‐term potentiation (LTP) comprise cellular processes that enable memory. Neuromodulators such as serotonin regulate hippocampal function, and the 5‐HT₄‐receptor contributes to processes underlying cognition. It was previously shown that in the CA1‐region, 5‐HT₄‐receptors regulate the frequency‐response relationship of synaptic plasticity: patterned afferent stimulation that has no effect on synaptic strength (i.e., a θm‐frequency), will result in LTP or LTD, when given in the presence of a 5‐HT₄‐agonist, or antagonist, respectively. Here, we show that in the dentate gyrus (DG) and CA3 regions of freely behaving rats, pharmacological manipulations of 5‐HT₄‐receptors do not influence responses generated at θm‐frequencies, but activation of 5‐HT₄‐receptors prevents persistent LTD in mossy fiber (mf)‐CA3, or perforant path‐DG synapses. Furthermore, the regulation by 5‐HT₄‐receptors of LTP is subfield‐specific: 5‐HT₄‐receptor‐activation prevents mf‐CA3‐LTP, but does not strongly affect DG‐potentiation. These data suggest that 5‐HT₄‐receptor activation prioritises information encoding by means of LTP in the DG and CA1 regions, and suppresses persistent information storage in mf‐CA3 synapses. Thus, 5‐HT₄‐receptors serve to shape information storage across the hippocampal circuitry and specify the nature of experience‐dependent encoding. © 2016 The Authors Hippocampus Published by Wiley Periodicals, Inc.

A novel versatile hybrid infusion-multielectrode recording (HIME) system for acute drug delivery and multisite acquisition of neuronal activity in freely moving mice

To characterize information transfer in defined brain circuits involving multiple brain regions and to evaluate underlying molecular mechanisms and their dysregulation in major brain diseases, a simple and reliable system is ultimately required for electrophysiological recording of local field potentials (LFPs, or local EEG) in combination with local delivery of drugs, enzymes and gene expression-controlling viruses near the place of recording. Here we provide a new design of a versatile reusable hybrid infusion-recording (HIME) system which can be utilized in freely moving mice performing cognitive tasks. The HIME system allows monitoring neuronal activity in multiple layers in several brain structures. Here, we provide examples of bilateral injection and recordings of full spectrum of learning and memory related oscillations, i.e., theta (4-12 Hz), gamma (40-100) and ripple activity (130-150 Hz), in five hippocampal layers as well as in the CA1 and CA2 regions. Furthermore, the system is designed to be used for parallel recordings in the amygdala, cortex and other brain areas, before and after infusion of reagents of interest, either in or off a cognitive test. We anticipate that the HIME system can be particularly convenient to advance functional neuroglycobiological studies and molecular deciphering of mechanisms governing long-term memory consolidation.

How the Body Talks to the Brain; Peripheral Mediators of Physical Activity-Induced Proliferation in the Adult Hippocampus

In the hippocampal dentate gyrus, stem cells maintain the capacity to produce new neurons into adulthood. These adult-generated neurons become fully functional and are incorporated into the existing hippocampal circuit. The process of adult neurogenesis contributes to hippocampal functioning and is influenced by various environmental, hormonal and disease-related factors. One of the most potent stimuli of neurogenesis is physical activity (PA). While the bodily and peripheral changes of PA are well known, e.g. in relation to diet or cardiovascular conditions, little is known about which of these also exert central effects on the brain. Here, we discuss PA-induced changes in peripheral mediators that can modify hippocampal proliferation, and address changes with age, sex or PA duration/intensity. Of the many peripheral factors known to be triggered by PA, serotonin, FGF-2, IGF-1, VEGF, β-endorphin and adiponectin are best known for their stimulatory effects on hippocampal proliferation. Interestingly, while age negatively affects hippocampal proliferation per se, also the PA-induced response to most of these peripheral mediators is reduced and particularly the response to IGF-1 and NPY strongly declines with age. Sex differences per se have generally little effects on PA-induced neurogenesis. Compared to short term exercise, long term PA may negatively affect proliferation, due to a parallel decline in FGF-2 and the β-endorphin receptor, and an activation of the stress system particularly during conditions of prolonged exercise but this depends on other variables as well and remains a matter of discussion. Taken together, of many possible mediators, serotonin, FGF-2, IGF-1, VEGF, β-endorphin and adiponectin are the ones that most strongly contribute to the central effects of PA on the hippocampus. For a subgroup of these factors, brain sensitivity and responsivity is reduced with age.

Physiology, signaling, and pharmacology of galanin peptides and receptors: three decades of emerging diversity

Galanin was first identified 30 years ago as a "classic neuropeptide," with actions primarily as a modulator of neurotransmission in the brain and peripheral nervous system. Other structurally-related peptides-galanin-like peptide and alarin-with diverse biologic actions in brain and other tissues have since been identified, although, unlike galanin, their cognate receptors are currently unknown. Over the last two decades, in addition to many neuronal actions, a number of nonneuronal actions of galanin and other galanin family peptides have been described. These include actions associated with neural stem cells, nonneuronal cells in the brain such as glia, endocrine functions, effects on metabolism, energy homeostasis, and paracrine effects in bone. Substantial new data also indicate an emerging role for galanin in innate immunity, inflammation, and cancer. Galanin has been shown to regulate its numerous physiologic and pathophysiological processes through interactions with three G protein-coupled receptors, GAL1, GAL2, and GAL3, and signaling via multiple transduction pathways, including inhibition of cAMP/PKA (GAL1, GAL3) and stimulation of phospholipase C (GAL2). In this review, we emphasize the importance of novel galanin receptor-specific agonists and antagonists. Also, other approaches, including new transgenic mouse lines (such as a recently characterized GAL3 knockout mouse) represent, in combination with viral-based techniques, critical tools required to better evaluate galanin system physiology. These in turn will help identify potential targets of the galanin/galanin-receptor systems in a diverse range of human diseases, including pain, mood disorders, epilepsy, neurodegenerative conditions, diabetes, and cancer.

Microfabricated sampling probes for in vivo monitoring of neurotransmitters

Microfabricated fluidic systems have emerged as a powerful approach for chemical analysis. Relatively unexplored is the use of microfabrication to create sampling probes. We have developed a sampling probe microfabricated in Si by bulk micromachining and lithography. The probe is 70 μm wide by 85 μm thick by 11 mm long and incorporates two buried channels that are 20 μm in diameter. The tip of the probe has two 20 μm holes where fluid is ejected or collected for sampling. Utility of the probe was demonstrated by sampling from the brain of live rats. For sampling, artificial cerebral spinal fluid was infused in through one channel at 50 nL/min while sample was withdrawn at the same flow rate from the other channel. Analysis of resulting fractions collected every 20 min from the striatum of rats by liquid chromatography with mass spectrometry demonstrated reliable detection of 17 neurotransmitters and metabolites. The small probe dimensions suggest it is less perturbing to tissue and can be used to sample smaller brain nuclei than larger sampling devices, such as microdialysis probes. This sampling probe may have other applications such as sampling from cells in culture. The use of microfabrication may also enable incorporation of electrodes for electrochemical or electrophysiological recording and other channels that enable more complex sample preparation on the device.

A prototype device for non-invasive continuous monitoring of intracerebral hemorrhage

A prototype for a non-invasive, real-time, monitoring device was developed to detect changes in the brain secondary to disease or injury such as intracerebral hemorrhage (ICH). The eventual goal is a non-invasive, real time sensor that can alert the clinician to alterations in the comatose patient's brain resulting from hemorrhage, seizure or stroke. In this work, a 400 MHz electromagnetic (EM) signal was transmitted with an antenna (T), incident on a 'brain gel' in vitro ICH model, and received by a receiving (R) antenna. Changes in the received signal were found to be induced by the presence of blood. The received power (P(R)) was found to be a linear function of the cross sectional area of blood, as measured normal to the incident wave. In addition, the sensor was able to detect as little as 1 mL of blood in this 1000 mL in vitro model.

Voluntary exercise offers anxiolytic potential and amplifies galanin gene expression in the locus coeruleus of the rat

Although exercise improves anxiety in humans, it is controversial whether exercise is anxiolytic in rodents. We tested the hypothesis that stress influences the effect of exercise on anxiety-like and defensive behaviors. To explore the neurobiological mechanisms of exercise, we also examined whether exercise alters gene expression for the stress-related peptide galanin. Rats were housed in the presence or absence of a running wheel for 21 d. A subset of these rats were (1) not injected or received a single high, dose of the β-carboline FG7142 (inverse agonist at the benzodiazepine receptor site) immediately prior to testing or (2) were injected repeatedly with vehicle or FG7142 during the last 10d of exercise. On day 22, anxiety-like and defensive behaviors were measured in the elevated plus maze, shock probe defensive burying, and defensive withdrawal tests. Locus coeruleus prepro-galanin mRNA was measured by in situ hybridization. Exercise and sedentary rats that were not injected exhibited similar behavior in all tests, whereas FG7142 injected immediately prior to the test battery produced intense avoidance and immobility consistent with an anxiety-like response. However, exercise produced anxiolytic-like and active defensive behaviors in the test battery relative to the sedentary condition in rats injected repeatedly with vehicle or FG7142. Exercise also increased prepro-galanin mRNA in the locus coeruleus relative to sedentary controls. These data suggest that the emergence of enhanced adaptive behavior after chronic voluntary exercise is influenced by stress. Our data support a role for galanin in the beneficial consequences of wheel running.

Galanin negatively modulates opiate withdrawal via galanin receptor 1

RATIONALE

The neuropeptide galanin has been shown to modulate opiate dependence and withdrawal. These effects could be mediated via activation of one or more of the three distinct G protein-coupled receptors, namely galanin receptors 1 (GalR1), 2 (GalR2), and 3 (GalR3).

OBJECTIVES

In this study, we used several transgenic mouse lines to further define the mechanisms underlying the role played by galanin and its receptors in the modulation of morphine dependence. First, transgenic mice expressing β-galactosidase under the control of the galanin promoter were used to assess the regulation of galanin expression in response to chronic morphine administration and withdrawal. Next, the behavioral responses to chronic morphine administration and withdrawal were tested in mice that over-express galanin, lack the GalR1 gene, or lack the GalR2 gene.

METHODS

Transgenic and matched wild-type mice were given increasing doses of morphine followed by precipitation of withdrawal by naloxone and behavioral responses to withdrawal were assessed.

RESULTS

Both morphine administration and withdrawal increased galanin gene transcription in the locus coeruleus (LC). Increasing galanin levels in the brain reduced signs of opiate withdrawal. Mice lacking GalR1 undergo more severe opiate withdrawal, whereas mice lacking GalR2 show no significant difference in withdrawal signs, compare with matched wild-type controls.

CONCLUSIONS

Opiate administration and withdrawal increase galanin expression in the LC. Galanin opposes the actions of morphine which leads to opiate dependence and withdrawal, an effect that is mediated via GalR1.

Cholinergic activation of hippocampal neural stem cells in aged dentate gyrus

Adult hippocampal neurogenesis contributes to the hippocampal circuit's role in cognitive functioning. New neurons are generated from hippocampal neural stem cells (NSCs) throughout life, but their generation is substantially diminished in aged animals due to a decrease in NSC proliferation. Because acetylcholine (ACh) is an important neurotransmitter released in the hippocampus during learning and exercise that is known to decrease with aging, we investigated whether aged NSCs can respond to ACh. In this study, we found that cholinergic stimulation has a positive effect on NSC proliferation in both young adult (8-12 weeks old) and aged mice (>2 years old). In fresh hippocampal slices, we observed a rapid calcium increase in NSCs in the dentate gyrus after muscarinic cholinergic stimulation, in both age groups. Furthermore, we found that the exercise-induced promotion of aged NSC proliferation was abrogated by the specific lesioning of the septal cholinergic system. In turn, cholinergic activation by either eserine (physostigmine) or donepezil treatment promoted the proliferation of NSCs in aged mice. These results indicate that NSCs respond to cholinergic stimulation by proliferating in aged animals. Physiological and/or pharmacological cholinergic stimulation(s) may ameliorate cognitive decline in aged animals, by supporting adult hippocampal neurogenesis.

Ultrasound-enhanced rt-PA thrombolysis in an ex vivo porcine carotid artery model

Ultrasound is known to enhance recombinant tissue plasminogen activator (rt-PA) thrombolysis. In this study, occlusive porcine whole blood clots were placed in flowing plasma within living porcine carotid arteries. Ultrasonically induced stable cavitation was investigated as an adjuvant to rt-PA thrombolysis. Aged, retracted clots were exposed to plasma alone, plasma containing rt-PA (7.1 ± 3.8 μg/mL) or plasma with rt-PA and Definity® ultrasound contrast agent (0.79 ± 0.47 μL/mL) with and without 120-kHz continuous wave ultrasound at a peak-to-peak pressure amplitude of 0.44 MPa. An insonation scheme was formulated to promote and maximize stable cavitation activity by incorporating ultrasound quiescent periods that allowed for the inflow of Definity®-rich plasma. Cavitation was measured with a passive acoustic detector throughout thrombolytic treatment. Thrombolytic efficacy was measured by comparing clot mass before and after treatment. Average mass loss for clots exposed to rt-PA and Definity® without ultrasound (n = 7) was 34%, and with ultrasound (n = 6) was 83%, which constituted a significant difference (p < 0.0001). Without Definity® there was no thrombolytic enhancement by ultrasound exposure alone at this pressure amplitude (n = 5, p < 0.0001). In the low-oxygen environment of the ischemic artery, significant loss of endothelium occurred but no correlation was observed between arterial tissue damage and treatment type. Acoustic stable cavitation nucleated by an infusion of Definity® enhances rt-PA thrombolysis without apparent treatment-related damage in this ex vivo porcine carotid artery model.

Mice lacking the galanin gene show decreased sensitivity to nicotine conditioned place preference

Previous work has indicated that the neuropeptide galanin decreases sensitivity to the rewarding effects of morphine and cocaine, but increases alcohol drinking. The aim of the current study was to examine the role of galanin signaling in nicotine reward by testing the effects of nicotine in mice lacking galanin peptide (GAL-/-) as compared to wild-type (GAL+/+) controls. Using an unbiased, three-chamber conditioned place preference (CPP) paradigm the dose-response function for nicotine CPP was tested in GAL-/- and GAL+/+ mice. Since activation of extracellular signal-related kinase (ERK2) is involved in the rewarding effects of several classes of drugs of abuse, we then measured the level of ERK2 phosphorylation in the nucleus accumbens shell (NACsh) and core (NACco) of GAL-/- and GAL+/+ mice following re-exposure to the CPP chamber previously paired with nicotine as a marker of mesolimbic system activation. Finally, we examined whether acute nicotine administration affects ERK2 activity in GAL-/- and GAL+/+ mice. GAL-/- mice required a higher dose of nicotine to induce a significant CPP compared to GAL+/+ mice. In the conditioning groups showing significant expression of nicotine CPP, only GAL+/+ mice showed ERK2 activation in the NACsh. This suggests that the nicotine CPP observed in GAL+/+ mice resulted in differential recruitment of ERK signaling in the NACsh compared to GAL-/- mice. In addition, no activation of ERK2 was observed following acute nicotine administration in either genotype. These data, along with prior results, suggest that galanin alters sensitivity to drugs of abuse differentially, with morphine, cocaine and amphetamine place preference suppressed, and nicotine and alcohol preference increased, by galanin signaling.

Effects of galanin on monoaminergic systems and HPA axis: Potential mechanisms underlying the effects of galanin on addiction- and stress-related behaviors

Like a number of neuropeptides, galanin can alter neural activity in brain areas that are important for both stress-related behaviors and responses to drugs of abuse. Accordingly, drugs that target galanin receptors can alter behavioral responses to drugs of abuse and can modulate stress-related behaviors. Stress and drug-related behaviors are interrelated: stress can promote drug-seeking, and drug exposure and withdrawal can increase activity in brain circuits involved in the stress response. We review here what is known about the ability of galanin and galanin receptors to alter neuronal activity, and we discuss potential mechanisms that may underlie the effects of galanin on behaviors involved in responses to stress and addictive drugs. Understanding the mechanisms underlying galanin's effects on neuronal function in brain regions related to stress and addiction may be useful in developing novel therapeutics for the treatment of stress- and addiction-related disorders.

Compartment-specific roles of ATP-binding cassette transporters define differential topotecan distribution in brain parenchyma and cerebrospinal fluid

Topotecan is a substrate of the ATP-binding cassette transporters P-glycoprotein (P-gp/MDR1) and breast cancer resistance protein (BCRP). To define the role of these transporters in topotecan penetration into the ventricular cerebrospinal fluid (vCSF) and brain parenchymal extracellular fluid (ECF) compartments, we performed intracerebral microdialysis on transporter-deficient mice after an intravenous dose of topotecan (4 mg/kg). vCSF penetration of unbound topotecan lactone was measured as the ratio of vCSF-to-plasma area under the concentration-time curves. The mean +/- SD ratios for wild-type, Mdr1a/b(-/-), Bcrp1(-/-), and Mdr1a/b(-/-)Bcrp1(-/-) mice were 3.07 +/- 0.09, 2.57 +/- 0.17, 1.63 +/- 0.12, and 0.86 +/- 0.05, respectively. In contrast, the ECF-to-plasma ratios for wild-type, Bcrp1(-/-), and Mdr1a/b(-/-)Bcrp1(-/-) mice were 0.36 +/- 0.06, 0.42 +/- 0.06, and 0.88 +/- 0.07. Topotecan lactone was below detectable limits in the ECF of Mdr1a/b(-/-) mice. When gefitinib (200 mg/kg) was preadministered to inhibit Bcrp1 and P-gp, the vCSF-to-plasma ratio decreased to 1.29 +/- 0.09 in wild-type mice and increased to 1.13 +/- 0.13 in Mdr1a/b(-/-)Bcrp1(-/-) mice, whereas the ECF-to-plasma ratio increased to 0.74 +/- 0.14 in wild-type and 1.07 +/- 0.03 in Mdr1a/b(-/-)Bcrp1(-/-) mice. Preferential active transport of topotecan lactone over topotecan carboxylate was shown in vivo by vCSF lactone-to-carboxylate area under the curve ratios for wild-type, Mdr1a/b(-/-), Bcrp1(-/-), and Mdr1a/b(-/-)Bcrp1(-/-) mice of 5.69 +/- 0.83, 3.85 +/- 0.64, 3.61 +/- 0.46, and 0.78 +/- 0.19, respectively. Our results suggest that Bcrp1 and P-gp transport topotecan into vCSF and out of brain parenchyma through the blood-brain barrier. These findings may help to improve pharmacologic strategies to treat brain tumors.

Serotonergic regulation of galanin-induced selective macronutrient intake in self-selecting rats

We investigated macronutrient intake after intraventricular injection of galanin (GAL, 3 nmol/5 microl/rat) and/or serotonin (5-HT, 50 nmol/5 microl/rat) in self-selecting fasted rats with preferences for either carbohydrates or fats. GAL injection significantly increased carbohydrate and total intake in all rats irrespective of macronutrient preference, whereas 5-HT alone did not affect macronutrient intake. The GAL-induced increase in total intake decreased to the level of saline controls when GAL was coinjected with 5-HT. The ratio of kilocalories of carbohydrates, fats and proteins (macronutrient energy ratio) after injections of GAL and/or 5-HT was similar to the saline control. In carbohydrate-preferring rats, GAL increased carbohydrate, protein and fat intake as well as total intake. Coinjection of GAL and 5-HT tended to decrease carbohydrate intake, but increase protein and fat intake. The macronutrient energy ratio after injection of GAL did not change, but the carbohydrate energy ratio decreased after 5-HT was injected, with or without GAL. In contrast, in fat-preferring rats, GAL significantly increased carbohydrate intake. Injection of 5-HT with or without GAL did not change total macronutrient intake. The macronutrient energy ratio did not change after GAL injection with or without 5-HT. These differences suggest that macronutrient preferences should be considered in any macronutrient intake study, and that serotonergic neurons play a part in the regulation of GAL-induced macronutrient intake.

Acetylcholine Release from Urinary Bladder Smooth Muscles of Non-Insulin-Dependent Diabetic Rats

INTRODUCTION

To investigate the mechanism of voiding dysfunction in non-insulin-dependent diabetes mellitus, we attempted to measure the acetylcholine (ACh) release using an in vivo microdialysis technique and measuring the detrusor pressure after electrical field stimulation (EFS) of the pelvic nerve.

MATERIALS AND METHODS

Eight- and 32-week-old female Goto-Kakizaki (GK) rats (non-insulin-dependent diabetes mellitus model) and age-matched female Wistar rats (controls) were used in this study. The pelvic nerve was exposed on a bipolar platinum electrode to EFS, and a cannula was inserted into the bladder to measure the detrusor pressure. The microdialysis probe was inserted into the bladder wall and was connected to a microinfusion syringe pump. Dialysate was constantly perfused, collected in a microtube, and then injected into the ACh assay system. Histological examinations were performed by staining with hematoxylin and eosin and S-100 immunohistochemical staining in bladder preparations of both GK and control rats.

RESULTS

In 8-week-old rats, both detrusor pressures and amounts of ACh release of GK rats were not significantly different from those of control rats. In 32-week-old rats, both detrusor pressures and ACh releases were only significantly increased at 5 and 10 Hz of EFS. In the histological study, the number of nerve fibers or bundles of 32-week-old GK rats was significantly decreased as compared with control rats.

CONCLUSION

The present data suggest that the decrease in EFS-induced ACh release in GK rats, which may be caused by the decreased number of nerve fibers, may contribute to the decrease in bladder contractions.

Cholinergic mechanisms involved in the pain relieving effect of spinal cord stimulation in a model of neuropathy

The mechanisms underlying the pain relieving effect of spinal cord stimulation (SCS) on neuropathic pain remain unclear. We have previously demonstrated that suppression of tactile hypersensitivity produced by SCS may be potentiated by i.t. clonidine in a rat model of mononeuropathy. Since the analgesic effect of this drug is mediated mainly via cholinergic mechanisms, a study exploring the possible involvement of the spinal cholinergic system in SCS was undertaken. The effect of SCS was assessed with von Frey filaments in rats displaying tactile hypersensitivity after partial ligation of the sciatic nerve and both SCS-responding and non-responding as well as normal rats were subjected to microdialysis in the dorsal horn. Acetylcholine (ACh) was analyzed with HPLC before, during and after SCS. SCS produced significantly increased release of ACh in the dorsal horn in rats responding to SCS whereas the release was unaffected in the non-responding animals. Furthermore, the basal release of ACh was significantly lower in nerve lesioned than in normal rats. In another group of rats it was found that the response to SCS was completely eliminated by i.t. atropine and a muscarinic M(4) receptor antagonist while a partial attenuation was produced by M(1) and M(2) antagonists. Blocking of nicotinic receptors did not influence the SCS effect. In conclusion, the attenuating effect of SCS on pain related behavior is associated with the activation of the cholinergic system in the dorsal horn and mediated via muscarinic receptors, particularly M(4,) while nicotinic receptors appear not to be involved.

Genetic variation in cortico-amygdala serotonin function and risk for stress-related disease

The serotonin system is strongly implicated in the pathophysiology and therapeutic alleviation of stress-related disorders such as anxiety and depression. Serotonergic modulation of the acute response to stress and the adaptation to chronic stress is mediated by a myriad of molecules controlling serotonin neuron development (Pet-1), synthesis (tryptophan hydroxylase 1 and 2 isozymes), packaging (vesicular monoamine transporter 2), actions at presynaptic and postsynaptic receptors (5-HT1A, 5-HT1B, 5-HT2A, 5-HT2C, 5-HT3A, 5-HT4, 5-HT5A, 5-HT6, 5-HT7), reuptake (serotonin transporter), and degradation (monoamine oxidase A). A growing body of evidence from preclinical rodents models, and especially genetically modified mice and inbred mouse strains, has provided significant insight into how genetic variation in these molecules can affect the development and function of a key neural circuit between the dorsal raphe nucleus, medial prefrontal cortex and amygdala. By extension, such variation is hypothesized to have a major influence on individual differences in the stress response and risk for stress-related disease in humans. The current article provides an update on this rapidly evolving field of research.

Recent advances in methods for the analysis of catecholamines and their metabolites

Catecholamines, for example epinephrine, norepinephrine, and dopamine, are widely distributed and are important neurotransmitters and hormones in mammalian species. Several methods have been developed for analysis of catecholamines and related compounds. Determination of catecholamines in biological fluids has enabled us to clarify the physiological role played by these amines. Catecholamine levels in plasma and/or urine are also useful for diagnosis of several diseases, for example hypertension, pheochromocytoma, and neuroblastoma. This review covers reports from 2000 to the present of methods for the analysis of catecholamines and their metabolites.

Derivatization chemistries for determination of serotonin, norepinephrine and dopamine in brain microdialysis samples by liquid chromatography with fluorescence detection

The present paper provides an overview on currently developed derivatization chemistries and techniques for determination of monoamine neurotransmitters serotonin (5-HT), norepinephrine (NE) and dopamine (DA) in microdialysis samples by microbore liquid chromatography with fluorescence detection. In mild alkaline conditions, 5-hydroxyindoles and catecholamines react with benzylamine (BA), forming highly fluorescent 2-phenyl-4,5-pyrrolobenzoxazoles and 2-phenyl(4,5-dihydropyrrolo) [2,3-f]benzoxazoles, respectively. However, for derivatization of DA a higher fluorescence intensity was achieved for reaction with 1,2-diphenylethylenediamine (DPE) rather than with BA, therefore for simultaneous determination of 5-HT, NE and DA in brain microdialysates, a two-step derivatization with BA followed by DPE was developed. The detection limits for 5-HT, NE and DA were 0.2, 0.08 and 0.13 fmol, respectively, in an injection volume of 20 microL, which corresponds to concentrations of 30, 12 and 19.5 pm, respectively in standard solution prior to derivatization. The experimental data presented demonstrate the ability of the technique to simultaneously monitor neuronally releasable pools of monoamine neurotransmitters in the rat and mouse brains at basal conditions and following pharmacological treatments or physiological stimuli. These techniques play an important role in drug discovery and clinical investigation of psychiatric and neurological diseases such as depression, schizophrenia and Parkinson's disease.

Role of galanin receptor 1 and galanin receptor 2 activation in synaptic plasticity associated with 3',5'-cyclic AMP response element-binding protein phosphorylation in the dentate gyrus: studies with a galanin receptor 2 agonist and galanin receptor 1 knockout mice

The neuropeptide galanin was shown to impair cognitive performance and reduce hippocampal CA1 long-term potentiation (LTP) in rodents. However, the contribution of the two main galanin receptors; GalR1 and GalR2, present in the hippocampus to these effects is not known. In the present study, we determined the protein expression levels of GalR1 and GalR2 in the mouse dentate gyrus (DG) and used galanin (2-11), a recently introduced GalR2 agonist, and GalR1 knockout mice to examine the contribution of GalR1 and GalR2 to the modulation of LTP and 3',5'-cyclic AMP response element-binding protein (CREB)-dependent signaling cascades. In the DG, 57+/-5% of the galanin binding sites were GalR2, and the remaining population corresponded to GalR1. In hippocampal slices, galanin (2-11) fully blocked the induction of DG LTP, whereas galanin (1-29), a high affinity agonist for both GalR1 and GalR2, strongly but not fully attenuated the late phase of LTP by 80+/-1.5%. Application of galanin (1-29) or galanin (2-11) after LTP induction caused a transient reduction in the maintenance phase of LTP, with the larger effect displayed by superfusion of galanin (2-11). The induction and maintenance of DG LTP was not altered in the GalR1 knockout mice. Superfusion of galanin (1-29) or galanin (2-11) blocked the LTP induction to the same degree indicating a role for GalR2 in the induction phase of DG LTP. Furthermore, we analyzed the effects of GalR1 and/or GalR2 activation on DG LTP-induced CREB phosphorylation, associated with the late transcriptional effects of LTP. In the lateral part of the granule cell layer, high-frequency trains stimulation caused a significant increase in the level of CREB phosphorylation, which was significantly reduced by application of either galanin (1-29) or galanin (2-11), indicating that both GalR1 and/or GalR2 can mediate some of their effects on LTP through inhibition of CREB-related signaling cascades.

A simple liquid chromatographic method based on intramolecular excimer-forming derivatization and fluorescence detection for the determination of tyrosine and tyramine in urine

A liquid chromatographic (LC) method for sensitive and selective fluorometric determination of p-hydroxyphenylethylamino group containing compounds is described. This method is based on an intramolecular excimer-forming fluorescence derivatization with a pyrene reagent, 4-(1-pyrene)butanoyl chloride, followed by reversed-phase LC. The analytes, containing an amino moiety and a phenolic hydroxyl moiety in a molecule, were converted to the corresponding dipyrene-labeled derivatives by one-step derivatization. The dipyrene-labeled derivatives afforded intramolecular excimer fluorescence (440-540 nm), which can clearly be discriminated from the normal fluorescence (360-420 nm) emitted from reagent blanks. The derivatives of tyrosine and tyramine could be separated by reversed-phase LC on ODS column under conditions of isocratic elution. The detection limits (signal-to-noise ratio = 3) for tyrosine and tyramine were 4.5 and 2.6 fmol per 20 microL injection, which corresponded to analyte concentrations of 0.9 and 0.5 nM, respectively.

Galanin impairs performance on learning and memory tasks: findings from galanin transgenic and GAL-R1 knockout mice

Galanin (GAL) impairs performance on cognitive tasks when administered centrally to rats. GAL transgenic (GAL-tg) mice overexpressing endogenous GAL show deficits on the probe trial of the Morris water maze spatial learning task, on the social transmission of food preference olfactory memory task, and on the trace cued fear conditioning emotional learning and memory task. Knockout mice deficient in the GAL-R1 receptor subtype were normal on most memory tasks, while showing a small deficit in trace cued fear conditioning, suggesting a selective role for the GAL-R1 in aversive memories, and implicating other GAL receptor subtypes in spatial learning and olfactory social memory. The growing body of rodent literature implicating excess GAL in cognitive impairment is relevant to the overexpression of GAL in the basal forebrain during the progression of Alzheimer's disease.

High-sensitive liquid chromatographic method for determination of neuronal release of serotonin, noradrenaline and dopamine monitored by microdialysis in the rat prefrontal cortex

A high-sensitive liquid chromatographic method based on precolumn derivatization and fluorescence detection allowing simultaneous determination of serotonin (5-HT), noradrenaline (NA) and dopamine (DA) in brain microdialysis samples is described. 5-HT, NA and DA were derivatized with benzylamine and 1,2-diphenylethylenediamine in the presence of potassium hexacyanoferrate(III) and glycine, which yielded to highly fluorescent and stable benzoxazoles. The derivatized samples were separated on a microbore column (150 mm x 1.0mm i.d., packed with C18 silica, 5 microm) within 60 min. The mobile phase consisted of acetonitrile-Briton-Robinson buffer (pH 7.2) (32:68, v/v) containing 5 mM Na2EDTA and 5 mM octanesulfonic acid sodium salt. The detection limits (signal-to-noise ratio of 3) for 5-HT, NA and DA were 76, 42 and 95 amol/10 microl injected on-column, respectively. Microdialysis samples were collected at 10-min intervals from the probes implanted in the prefrontal cortex of awake rats. The basal levels of 5-HT, NA and DA were 7.3 +/- 0.7, 5.3 +/- 0.31 and 8.1 +/- 0.47 fmol/5 microl (mean +/- S.E.M., n = 5). Following 90-min perfusion with tetrodotoxin (1 microM) or calcium-free Ringer solution, the DA and NA levels were reduced to about 15 and 20%, respectively and the 5-HT levels to 45 and 60% of the basal levels, respectively. Reserpine, 12h after a dose of 5mg/kg i.p., reduced the extracellular 5-HT, NA and DA concentrations to about 34, 39 and 32% of the basal levels, respectively. In conclusion, the preset microdialysis/analytical method enables simultaneous monitoring of basal and pharmacologically reduced neuronal release of 5-HT, NA and DA in the rat brain.

Phenotypic assessment of galanin overexpressing and galanin receptor R1 knockout mice in the tail suspension test for depression-related behavior

RATIONALE

Galanin and its receptors exert inhibitory neuromodulatory control over brain monoamines. Rat studies revealed that galanin expression is upregulated by exposure to stressors and that galanin manipulations modify neuroendocrine and behavioral responses to stress, leading to the hypothesis that galanin mediates depression-related behaviors.

METHODS

In the present study, we examined the role of galanin in modulating antidepressant-related behavior in galanin overexpressing transgenic (GAL-tg) mice and galanin receptor R1 knockout (GAL-R1 KO) mice, using the tail suspension test (TST). Quantitative autoradiography for 5-HT(1A)-R and serotonin transporter binding density tested for changes in these two major regulatory components of the 5-HT system in galanin mutant mice.

RESULTS

Baseline TST behavior was normal in GAL-tg and GAL-R1 KO mice, and intracerebroventricular administration of galanin failed to alter TST behavior in normal C57BL/6J mice. The TST anti-immobility effects of acute treatment with the serotonin reuptake inhibitor, fluoxetine (0-30 mg/kg), and the norepinephrine reuptake inhibitor, desipramine (0-30 mg/kg), were unaltered in galanin mutant mice. Hippocampal 5-HT(1A)-R density was significantly elevated in GAL-tg and GAL-R1 KO mice, while hippocampal 5-HTT density was reduced in GAL-R1 KO mice, relative to controls.

CONCLUSION

Neither pharmacological nor molecular genetic manipulations of galanin altered depression-related profiles in the TST. Possible functional alterations in hippocampal 5-HT neurotransmission may have contributed to these negative results. These preliminary findings provide evidence against the hypothesis that galanin plays a central role in mouse depression-related behaviors. It remains possible that galanin modulates depression-related responses in other experimental paradigms and species.

Microbore HPLC method with online microdialysis for measurement of topotecan lactone and carboxylate in murine CSF

We developed a chromatography method to measure lactone and carboxylate forms of topotecan (TPT) in mouse cerebrospinal fluid (CSF) using microdialysis sampling. The chromatography method utilized a microbore (0.8 mm) column. Analytes, which eluted in less than 5 min, were detected with a fluorescence detector. The calibration range was 0.25-100.0 ng/mL for both forms. The within-day and between-day precision was < or =16% for 0.8 ng/mL and < or =8.0% for 3, 12, and 80 ng/mL. Accuracy was +/-15% (0.8 and 3 ng/mL) and +/-10% (12 and 80 ng/mL). TPT lactone hydrolyzes to the carboxylate during sampling, so we developed an equation and parameters to describe the TPT lactone hydrolysis in artificial CSF (aCSF). After TPT administration, CSF dialysate samples (2 microL) were analyzed for lactone and carboxylate using online injection. The hydrolysis of each dialysate sample was then estimated and a correction applied. We conclude that this HPLC method coupled with online microdialysis sampling allows for the rapid measurement of both TPT forms in small volumes of murine CSF dialysate. The system allows for the determination of TPT pharmacokinetics in murine CSF and provides a tool to extend pharmacological studies in this brain compartment.

Effects of isoflurane on prefrontal acetylcholine release and hypothalamic Fos response in young adult and aged rats

This experiment investigated the influence of age on prefrontal acetylcholine (ACh) release and Fos response in the hypothalamic paraventricular nucleus and the nucleus tractus solitarius (NTS) of rats following isoflurane anesthesia. It is known that isoflurane decreases acetylcholine release in most brain regions. In the present study, we found that the level of prefrontal acetylcholine was significantly lower in 28-month-old rats (14% of baseline) than in 3-month-old rats (38% of baseline) during 2 h of isoflurane anesthesia (P < 0.05). The old rat group showed significantly greater Fos induction in the paraventricular nucleus compared to the young adult rat group (P < 0.05), indicating that the old rats were subjected to stress. No difference in Fos response was noted in the nucleus tractus solitarius. The old rats displayed a significant increase in feeding behavior during the 3-h recovery period (P < 0.05), but there was no difference in overall acetylcholine levels. Taken together, these findings suggest that isoflurane anesthesia influences old rats more profoundly than young adult rats with regard to reductions in acetylcholine release and stress responses. This may have implications for understanding the development of postoperative delirium in aged patients.

Distribution of galanin and galanin transcript in the brain of a galanin-overexpressing transgenic mouse

The distribution of galanin mRNA-expressing cells and galanin-immunoreactive (IR) cell bodies and processes was studied in the brain of mice overexpressing galanin under the PDGF-B promoter (GalOE mice) and of wild type (WT) mice, both in colchicine-treated and non-treated animals. In this abstract, we only describe the results in GalOE mouse. A widespread ectopic expression of galanin (both mRNA and peptide) was found, that is a situation when neither transcript nor peptide could be seen in WT mice, not even after colchicine treatment. However, in some regions, such as claustrum, basolateral amygdala, thalamus, CA1 pyramidal cells, and Purkinje cells only galanin mRNA could be detected. In the forebrain galanin was seen in the mitral cells of the olfactory bulb, throughout the cortex, in the basolateral amygdaloid nucleus, claustrum, granular and pyramidal cell layers of the hippocampus, subiculum and presubiculum. In the thalamus, the anterodorsal, mediodorsal, intermediodorsal and mediodorsal lateral nuclei, the reuniens and reticular nuclei showed ectopic expression of galanin. Within the hypothalamus, neurons of the suprachiasmatic nucleus contained galanin. In the mesencephalon, the geniculate nucleus, nucleus ruber, the mesencephalic trigeminal and reticulotegmental nuclei ectopically expressed galanin. In the cerebellum, galanin was observed in the Purkinje cells and in the lateral and interposed cerebellar nuclei. In the pons, sensory and motor nuclei of the trigeminal nerve, the laterodorsal and dorsal tegmental nuclei, the pontine, reticulotegmental and gigantocellular reticular nuclei expressed galanin. Within the medulla oblongata, labeled cells were detected in the facial, ambiguus, prepositus, lateral paragigantocellular and lateral reticular nuclei, and spinal trigeminal nucleus. High densities of galanin-IR fibers were found in the axonal terminals of the lateral olfactory tract, the hippocampal and presumably the cerebellar mossy fibers system, in several thalamic and hypothalamic regions and the lower brain stem. Possible functional consequences of galanin overexpression are discussed.

Selective reduction in ventral hippocampal acetylcholine release in awake galanin-treated rats and galanin-overexpressing transgenic mice

The neuropeptide galanin is an inhibitory modulator of hippocampal acetylcholine (ACh) release and cognitive functions. Anatomical evidence demonstrated some differences between the dorsal and ventral hippocampi notably in the expression of galanin receptor subtypes, and the neuronal population on which galanin-like immunoreactivity is expressed. This is suggestive of a differential role for this peptide in these two areas of the hippocampal formation. Using in vivo microdialysis, we investigated the role of galanin on ACh release in the dorsal and ventral hippocampi. Two models were studied: galanin-administered rats and transgenic mice over-expressing galanin (GAL-tg). In rats, galanin (2.0 and 10.0 microM) infused locally through the dialysis probe induced a significant decrease in ACh release in the ventral hippocampus, confirming previous findings, while no effect was seen in the dorsal hippocampus. Using the no net flux method, a significant reduction in ACh levels was noted only in the ventral hippocampus of GAL-tg compared to wild-type littermates. These results suggest that excess endogenous galanin can suppress basal ACh release, with anatomical specificity, to the ventral hippocampus. These results are of interest in the context of galanin receptor subtypes in the dorsal and ventral hippocampus, and the differential alterations of hippocampal subregions in neurological diseases such as Alzheimer's dementia.

The Modulatory Effect of Pyrethroids on Acetylcholine Release in the Hippocampus of Freely Moving Rats

The peripheral effects of pyrethroids on Na(+) channels are well known but the effects on CNS neurotransmission are less known. In the present study, type I and II pyrethroids were found to affect the release of acetylcholine (ACh) from hippocampus in freely moving rats as measured by in vivo microdialysis. The basal release of ACh from the hippocampus of untreated rats was 6.6 pmol/10 microl/10 min. Allethrin had an interesting dual effect on ACh release, increasing ACh efflux (to about 300% of baseline) at the lower dose of 20 mg/kg i.p. with a peak time of 60 min and decreasing the efflux (to about 40% of baseline) at the higher dose of 60 mg/kg i.p. up to 3 h after administration. Cyhalothrin 20 and 60 mg/kg i.p. inhibited the release (to about 30% of baseline) dose-dependently, with a peak time of 50-60 min after administration. Deltamethrin 20 mg/kg i.p. increased the efflux (to about 250% of baseline) with a peak time of 30 min after administration and 60 mg/kg i.p. increased the efflux (to about 450% of baseline) and remained at a steady level during the rest of the 3 h experiment. Control vehicle injections had no effect on the efflux of ACh in any of the experiments. This is the first report, using in vivo microdialysis, that pyrethroids modulate the ACh release in the hippocampus of rat brain.

Determination of serotonin, noradrenaline, dopamine and their metabolites in rat brain extracts and microdialysis samples by column liquid chromatography with fluorescence detection following derivatization with benzylamine and 1,2-diphenylethylenediamine

A highly selective and sensitive column liquid chromatographic method for fluorescence determination of serotonin (5-HT), dopamine (DA), noradrenaline (NA) and their related metabolites 5-hydroxyindole-3-acetic acid (5-HIAA) and 3,4-dihydroxyphenylacetic acid (DOPAC) following derivatization with benzylamine and 1,2-diphenylethylenediamine (DPE) is described. The monoamines and the metabolites (20 microl samples) were derivatized in a two-step reaction, initiated with 20 microl of 0.3M benzylamine in 0.3M 3-cyclohexylaminopropanesulfonic acid (CAPS) buffer (pH 10.0), (for 5-HT, 5-HIAA, 2 min, 24 degrees C) and followed by 20 microl of 0.1M DPE in 0.3M glycine buffer (pH 10.0), (for DA, NA, DOPAC, 20 min, 50 degrees C). Both reagents contained 0.02 M potassium hexacyanoferrate(III) and 50% (v/v) methanol. The resulting highly fluorescent and stable benzoxazole derivatives were isocratically separated on a reversed-phase column (150 mm x 1.5 mm i.d., packed with C18 silica, 5 microm) within 45 min. Using fluorescence detection at ex. and em. wavelengths of 345 and 480 nm, respectively, the detection limit (signal-to-noise ratio of 3) for 5-HT, DA, NA, 5-HIAA, L-DOPA and DOPAC ranged between 0.08 and 5.65 fmol per 20-microl injection (12-847.5 pM in standard solution). The concentrations of monoamines (expressed in microg/g wet weight, mean +/- S.E.M., n=5) in tissue extracts from the rat striatum were: 0.45+/-0.05 (5-HT), 4.27+/-0.08 (DA), 0.27+/-0.04 (NA), 0.55+/-0.06 (5-HIAA), 1.26+/-0.16 (L-DOPA) and 1.62+/-0.11 (DOPAC). Microdialysis samples were collected in 20 min intervals from the probes implanted in the striatum of awake rats. The basal monoamine levels (in fmol/20 microl, mean +/- S.E.M., n=5) in the dialysates were: 4.0+/-0.7 (5-HT), 78.4+/-9.1 (DA), 6.4+/-0.8 (NA), 785.5+/-64.5 (5-HIAA) and 5504.5+/-136.5 (DOPAC). It is concluded that the new fluorescence derivatization protocol provides an excellent means for simultaneous determination of all three monoamines both in the complex samples (e.g. brain homogenates) and also at trace levels, such as those found in the microdialysis samples.

Differential effects of (R)-, (R, S)- and (S)-8-hydroxy-2-(di-n-propylamino)tetralin on hippocampal serotonin release and induction of hypothermia in awake rats

The effects of (R)- and (S)-optical isomers of 8-hydroxy-2-(di-n-propylamino)-tetralin (8-OH-DPAT) and of the racemate (R,S)-8-OH-DPAT on serotonin (5-HT) release in the ventral hippocampus of awake rats and on induction of the whole-body hypothermia were studied. Extracellular 5-HT levels were determined by a newly developed high-sensitive HPLC method based on derivatization with benzylamine and fluorescence detection. The basal levels of 5-HT in 20 min microdialysates from rats perfused with Ringer solution or with Ringer solution containing 1 microM citalopram were 6.3 +/- 1.3 fmol/20 microl and 36.1 +/- 4.2 fmol/20 microl (n=20), respectively. The reduction of hippocampal 5-HT levels induced by subcutaneous (s.c.) administration of (R,S)-8-OH-DPAT (0.3 mg/kg) was significantly attenuated by the presence of 5-HT reuptake inhibitor citalopram in Ringer solution only at its peak value at 40 min (maximal reduction to 60% compared to 46% of control values in Ringer-perfused rats), whereas the overall effects were comparable at both experimental conditions. Injection of (R)-8-OH-DPAT (0.3 mg/kg s.c.) caused further reduction of 5-HT levels, to 49% and 41%, respectively, whereas (S)-8-OH-DPAT (0.3 mg/kg s.c.) caused maximal reduction of 5-HT levels only to 74% of controls in both perfusion groups. Similar pattern and time-courses were observed in rats with hypothermia induced by injection of 8-OH-DPAT enantiomers, where (R,S), (R)-forms were about two-times more potent than the (S)-isomer. It is concluded that the acute systemic dose of (R)-, (S)- and (R,S)-8-OH-DPAT enantiomers exerted enantiomer-specific effects on 5-HT(1A) receptor-mediated function both at the presynaptic and postsynaptic sites as revealed by monitoring hippocampal 5-HT levels and body temperature.

Enhanced hippocampal noradrenaline and serotonin release in galanin-overexpressing mice after repeated forced swimming test

Basal and forced swimming (FS) stress-induced release of noradrenaline (NA) and serotonin (5-HT) were determined by in vivo microdialysis in the ventral hippocampus of mice overexpressing galanin under the platelet-derived growth factor B promoter (GalOE/P) or under the dopamine beta-hydroxylase promoter (GalOE/D) (only NA). WT mice served as controls. Intraventricular infusion of galanin significantly reduced basal extracellular NA in WT mice and in GalOE/P mice (albeit less so). Microdialysis sampling during a 10-min FS showed that NA and 5-HT release were elevated to 213% and 156%, respectively, in the GalOE/P group, whereas in the WT group the increases were only 127% and 119%, respectively. The second (repeated) 10-min FS (RFS) caused a marked enhancement of NA and 5-HT release in the GalOE/P mice to 344% and 275%, respectively. However, the RFS caused only a 192% increase of extracellular NA levels in the GalOE/D mice. Pretreatment with the putative peptidergic galanin receptor antagonist M35 almost completely blocked the elevation of NA and 5-HT levels in the GalOE/P after RFS. These results suggest that the NA and 5-HT hippocampal afferents in GalOE/P mice are hypersensitive to both conditioned and unconditioned stressful stimuli, such as FS, and that this effect is mediated by galanin receptors. The present findings support a role of galanin in the regulation of release of NA and 5-HT, two neurotransmitters involved in mood control.

Simultaneous determination of 5-hydroxyindoles and catechols by high-performance liquid chromatography with fluorescence detection following derivatization with benzylamine and 1,2-diphenylethylenediamine

A highly selective and sensitive method for the simultaneous determination of 5-hydroxyindoles and catechols (serotonin, norepinephrine, dopamine and related compounds) by high-performance liquid chromatography with fluorescence detection is described. The method is based on the two-step precolumn derivatization of 5-hydroxyindoles and catechols with benzylamine (BA) and 1,2-diphenylethylenediamine (DPE), respectively, resulting in highly fluorescent and stable benzoxazole derivatives. The first derivatization with BA proceeds at room temperature (ca. 23 degrees C) for 2 min in a mixture of 0.3 M 3-cyclohexylamino-1-propanesulfonic acid buffer (pH 10.0) and methanol in the presence of potassium hexacyanoferrate(III). The subsequent second derivatization with DPE is carried out at 50 degrees C for 20 min in the presence of glycine. The resulting fluorescent derivatives of five 5-hydroxyindoles and seven catechols are separated on a reversed-phase column (150 x 1.5 mm I.D., packed with C18 silica, 5 microm) with isocratic elution using a mixture of acetonitrile-15 mM acetate buffer (pH 4.5) (34:66, v/v) containing 1 mM octanesulfonic acid sodium salt, and are detected spectrofluorimetrically at 480 nm with excitation at 345 nm. The detection limits (signal-to-noise ratio of 3) of the related compounds are 80 amol to 86 fmol for a 20-microl injection.

Effects of the nitric oxide donor, DEA/NO on cortical spreading depression

Cortical spreading depression (CSD) is a transient disruption of local ionic homeostasis that may promote migraine attacks and the progression of stroke lesions. We reported previously that the local inhibition of nitric oxide (NO) synthesis with Nomega-nitro-L-arginine methyl ester (L-NAME) delayed markedly the initiation of the recovery of ionic homeostasis from CSD. Here we describe a novel method for selective, controlled generation of exogenous NO in a functioning brain region. It is based on microdialysis perfusion of the NO donor, 2-(N,N-diethylamino)-diazenolate-2-oxide (DEA/NO). As DEA/NO does not generate NO at alkaline pH, and as the brain has a strong acid-base buffering capacity, DEA/NO was perfused in a medium adjusted at alkaline (but unbuffered) pH. Without DEA/NO, such a microdialysis perfusion medium did not alter CSD. DEA/NO (1, 10 and 100 microM) had little effect on CSD by itself, but it reversed in a concentration-dependent manner the effects of NOS inhibition by 1 mM L-NAME. These data demonstrate that increased formation of endogenous NO associated with CSD is critical for subsequent, rapid recovery of cellular ionic homeostasis. In this case, the molecular targets for NO may be located either on brain cells to suppress mechanisms directly involved in CSD genesis, or on local blood vessels to couple flow to the increased energy demand associated with CSD.

Galanin GAL-R1 receptor null mutant mice display increased anxiety-like behavior specific to the elevated plus-maze

The neuropeptide galanin coexists with norepinephrine and serotonin in neural systems mediating emotion. Previous findings suggested that galanin modulates anxiety-related behaviors in rodents. Three galanin receptor subtypes have been cloned; however, understanding their functions has been limited by the lack of galanin receptor subtype-selective ligands. To study the role of the galanin GAL-R1 receptor subtype in mediating anxiety-related behavior, we generated mice with a null mutation in the Galr1 gene. GAL-R1 -/- are viable and show no abnormalities in health, neurological reflexes, motoric functions, or sensory abilities. On a battery of tests for anxiety-like behavior, GAL-R1 -/- showed increased anxiety-like behavior on the elevated plus-maze test. Anxiety-related behaviors on the light/dark exploration, emergence, and open field tests were normal in GAL-R1 -/-. This test-specific anxiety-like phenotype was confirmed in a second, independent cohort of GAL-R1 null mutant mice and +/+ controls. Principal components factor analysis of behavioral scores from 279 mice suggested that anxiety-like behavior on the elevated plus-maze was qualitatively distinct from behavior on other tests in the battery. In addition, exposure to the elevated plus-maze produced a significantly greater neuroendocrine response than exposure to the light/dark exploration test, as analyzed in normal C57BL/6J mice. These behavioral findings in the first galanin receptor null mutant mouse are consistent with the hypothesis that galanin exerts anxiolytic actions via the GAL-R1 receptor under conditions of relatively high stress.

Catecholaminergic microcircuitry controlling the output of airway-related vagal preganglionic neurons

In this study, we have investigated the ultrastructure and function of the catecholaminergic circuitry modulating the output of airway-related vagal preganglionic neurons (AVPNs) in ferrets. Immunoelectron microscopy was employed to characterize the nature of catecholaminergic innervation of AVPN at the ultrastructural level. In addition, immunofluorescence was used to examine the expression of the alpha(2A)-adrenergic receptor (alpha(2A)-AR) on AVPNs, and norepinephrine release within the rostral nucleus ambiguous (rNA) was measured by using microdialysis. Physiological experiments were performed to determine the effects of stimulation of the noradrenergic locus coeruleus (LC) cell group on airway smooth muscle tone. The results showed that 1) catecholaminergic nerve endings terminate in the vicinity of identified AVPNs but very rarely form axosomatic or axodendritic synapses with the AVPNs that innervate the extrathoracic trachea; 2) AVPNs express the alpha(2A)-AR; 3) LC stimulation-induced norepinephrine release within the rNA region was associated with airway smooth muscle relaxation; and 4) blockade of alpha(2A)-AR on AVPNs diminished the inhibitory effects of LC stimulation on airway smooth muscle tone. It is concluded that a noradrenergic circuit originating within the LC is involved in the regulation of AVPN activity within the rNA, and stimulation of the LC dilates the airways by the release of norepinephrine and activation of alpha(2A)-AR expressed by AVPNs, mainly via volume transmission.

Galanin attenuates basal and antidepressant drug-induced increase of extracellular serotonin and noradrenaline levels in the rat hippocampus

Galanin is co-localized with classical neurotransmitters, such as acetylcholine, serotonin (5-HT) and noradrenaline (NA) in neurons or in brain regions implicated in cognitive and affective behaviour. In the present study, the effects of galanin on extracellular 5-HT and NA levels in the rat hippocampus were measured by in vivo microdialysis under basal conditions and following systemic administration of antidepressant drugs. Galanin (1.5 nmol i.c.v.) reduced basal 5-HT and NA levels to 65% and 86% of controls, respectively. Galanin (0.5 and 1.5 nmol i.c.v.) dose-dependently attenuated the elevation of 5-HT concentrations induced by imipramine and citalopram (10 mg/kg i.p., each) from 350% to 312% and from 230% to 160%, respectively. Galanin at 1.5 nmol transiently attenuated the effect of desipramine-induced (10 mg/kg i.p.) increase in extracellular NA levels from a maximal increase of 389-296% of the predrug levels. It is concluded that intraventricularly administered galanin attenuated both basal 5-HT and NA release and antidepressant drug-induced accumulation of extracellular 5-HT and NA levels most likely via a predominant inhibitory action on serotonergic and noradrenergic neurons in the raphe and locus coeruleus, respectively. These results further emphasize a possible role of galanin in regulation of 5-HT and NA neurotransmission in depressive states and during the course of antidepressant therapy.